$ { {-3} \times \left[\begin{array}{r}{3} \\ {4} \\ {1}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{-3}\times{3} \\ {-3}\times{4} \\ {-3}\times{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{-9} \\ {-12} \\ {-3}\end{array}\right]}$